Microsoft and Yahoo are selling political campaigns the ability to target voters online with tailored ads using names, Zip codes and other registration information that users provide when they sign up for free email and other services.

The Web giants provide users no notification that their information is being used for political targeting.

In one sense, campaigns are doing a more sophisticated version of what they’ve always done through the post office 2014 sending political fliers to selected households. But the Internet allows for more subtle targeting. It relies not on email but on advertisements that surfers may not realize have been customized for them.

Campaigns use voters records to assemble lists of people they’re trying to reach 2014 for instance, “registered Republicans that have made a donation,” Yahoo’s director of sales Andy Cotten told ProPublica. Microsoft and Yahoo help campaigns find these people online and then send them tailored ads.